With the development in networks, there are many electronic commerce systems to conduct commercial transactions through networks. In such a commerce system, a certain sort of valuable information such as cash is exchanged between machines on both ends engaged in a communication. Meanwhile, in recent years, a content usage right exchanged between machines in a content distribution system in which contents other than cash are distributed electronically has been witnessed.
In such a license information exchange system between machines, processing to be performed in the event of communication failure is a problem to be tackled, for license information is not to be subjected to unauthorized duplication or loss.
As a conventional license information exchange system with robustness against communication failure, there is a method disclosed in the Mondex patent (U.S. Pat. No. 5,982,293) in which the contents of a communication carried out between machines is recorded as a log so as to restore the exchange procedure of license information in the event of communication failure. Effective when license information is exchanged between two electronic purses, this method has a serious problem when used for a server-client type license information exchange system in which a number of client machines are connected to a single server.
This is because the server needs to communicate with a number of client machines at a time, leading to a highly increased size of the log data, as well as because a server-client communication is far more vulnerable than a communication between electronic purses, which consequently results in a higher occurrence rate of communication failure.
In order to solve these problems, the present invention aims at providing a license information exchange system capable of exchanging license information correctly in a server-client communication for exchanging license information such as content usage license information, even if communication failure occurs in the middle of such communication.
The present invention further aims at providing a license information exchange system capable of reducing the processing load on a license information exchange communication by reducing the number of communications carried out between a server and a client machine, and the number of data writings to a storage device of a server/client machine.